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1 Department of Cardiovascular
Medicine,
Nitric oxide (NO) donors inhibit sympathetic
neurotransmission and baroreceptor activity and can directly stimulate
heart rate (HR) in vitro. To assess whether exogenous NO affects
cardiovascular autonomic control in humans, we tested the
baroreceptor-cardiac reflex [baroreflex sensitivity (BRS)]
and the arterial blood pressure (BP) and HR variability during an
infusion of the NO donor sodium nitroprusside (SNP, 2 µg · kg
1 · min
1)
or 5% glucose in 16 healthy subjects. The hypotensive action of SNP
was prevented by phenylephrine (PE, 0.9 ± 0.15 µg · kg
1 · min
1).
The SNP + PE infusion did not affect BRS or HR variability, but it
caused a significant reduction in the diastolic and systolic BP
low-frequency power. In addition, SNP + PE caused a sustained 12%
increase in HR in the absence of changes in brachial and aortic BP. In
conclusion, SNP had no effect on the cardiac-vagal limb of the
baroreflex in humans but caused a substantial reduction in BP
low-frequency power consistent with a decreased baroreflex/sympathetic control of peripheral resistance. The increase in HR in the absence of
baroreceptor downloading confirms our previous finding of a direct
positive chronotropic effect of NO donors.
nitric oxide donors; heart rate; baroreceptors; blood pressure variability
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